The invention relates to a method for detecting misfire in the combustion chamber of an internal combustion engine.
This copending patent application is assigned to the assignee of the present application. Its disclosure is incorporated herein by reference.
It is explained in the copending patent application that normal combustion in the combustion chamber results in energy being transferred to the engine housing in the form of vibrations. If the combustion energy varies more than a predetermined amount, corrective action is taken by appropriately adjusting the air/fuel ratio, the spark timing, or the exhaust gas recirculation.
Using the accelerometer, the characteristics of the combustion event can be monitored and corrective action can be taken if the accelerometer data sampled during a defined crankshaft position window in which combustion is known to occur does not conform to a known relationship between accelerometer data and combustion energy during normal combustion.
It is known design practice to identify a misfire by monitoring crankshaft acceleration. This is done by using angular velocity data from a crankshaft position sensor, which can identify a change in acceleration due to combustion as well as absence of combustion. Absence of combustion would be an indicator of a misfire in a particular cylinder. One shortcoming of such prior art systems for identifying misfire using crankshaft acceleration data is that the data is sensitive to driveline induced vibrations resulting from road surface irregularities, gear changes, accessory loads, etc. Such prior art systems are incapable of distinguishing between a filtered crankshaft acceleration output signal caused by a misfire from a similar signal caused by a driveline induced disturbance not associated with a misfire.
It is an objective of the present invention to provide a misfire detection method for internal combustion engines that is capable of establishing a reliable misfire signal that is distinguished from acceleration data correlated to driveline disturbances not related to a combustion event.
It is a further objective of the invention to provide a reliable misfire detection method wherein a particular cylinder of a multiple cylinder engine can be identified as the source of misfire information.
The method steps include measuring engine vibration energy caused by combustion by processing accelerometer data, measuring instantaneous crankshaft and camshaft positions, determining the combustion chamber of a multiple cylinder engine in which combustion is expected to occur, determining whether combustion has occurred using both accelerometer data and crankshaft acceleration data, and determining whether a misfire has occurred by comparing processed accelerometer data with processed crankshaft position data.
The invention uses some steps of the technique involved in the measurement of mean effective combustion chamber pressure disclosed in the previously identified copending patent application. The present technique requires accelerometer data obtained from an engine mounted accelerometer to be processed simultaneously in parallel relationship with respect to the processing of crankshaft acceleration data obtained from a crankcase angular velocity sensor. Each control routine will determine if combustion has occurred in a particular combustion chamber of the multiple cylinder engine. If misfire appears to have occurred, as demonstrated by the output of each of the routines processed in parallel, then a reliable misfire signal will have been detected. Corrective action then can be taken to eliminate the condition that caused the misfire.
The invention is capable of obtaining a reliable misfire signal throughout the entire range of engine loads rather than in only a narrow range of selected loads, as in certain prior art systems.
If the output of the accelerometer does not detect a misfire but a misfire is detected by crankshaft acceleration data, the adaptive portion of the control routine of the invention will decrease the operating threshold for the measurement of misfire using the accelerometer. If the decrease in the threshold during the next control loop of the microprocessor results in the development of a misfire signal, the misfire signal will be considered to be reliable, and appropriate steps can be taken to eliminate the misfire condition. If the data from the accelerometer results in the determination of a misfire, but the data from the crankshaft acceleration processing routine does not indicate a misfire, the threshold for the accelerometer data is increased. This is a further adaptive step that is carried out in order to ensure reliable detection of a misfire.